Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $81.64   7.414%   $87.6928   $87.69   $87.70   $87.70  
  Purchase #2 $165.45   6.762%   $176.6377   $176.64   $176.65   $176.60  
  Purchase #3 $96.84   12.281%   $108.7329   $108.73   $108.75   $108.70  
  Purchase #4 $218.68   11.293%   $243.3755   $243.38   $243.40   $243.40  
  Purchase #5 $89.65   10.687%   $99.2309   $99.23   $99.25   $99.20  
  Purchase #6 $165.70   6.690%   $176.7853   $176.79   $176.80   $176.80  
  Purchase #7 $144.95   6.428%   $154.2674   $154.27   $154.25   $154.30  
  7 purchase totals = $962.91       $1,046.7225   $1,046.73   $1,046.80   $1,046.70